The Río San Juan was once critical to the entire region, the river was the main route of access to the entire country. Wide and navigable the river allowed hundreds of miles of thick tropical jungle to be easily transited. People and cargoes could be shipped from the Caribbean to the enormous Lake Nicaragua and the rich farmlands of central Nicaragua. Together the river and lake offered an easy crossing of the isthmus, allowing passengers and cargo to pass between the Atlantic and Pacific Oceans. At the northern end of Lake Nicaragua is Grenada, this old colonial city was the crown jewel of the region, where the treasures of the New World were amassed before shipment to Spain.
Defense of this critical river link proved to be necessary in the tumultuous history of the region. On several occasions pirate forces passed this way to loot and burn Grenada. In response to these incursions the Spanish selected a site on a high bluff and overlooking a significant set of rapids on the river as the ideal site for a defensive fortification. A large stone fort was built here, completed in 1675, becoming the lynch-pin for defending this critical access route to the interior of Nicaragua.
Somehow the name Fortress of the Immaculate Conception just does not bring to mind any form of military installation. Despite the name, this fortress is an impressive fortification, easily equivalent to the best contemporary fortifications elsewhere, quite a surprise as the location is and was quite remote. Most photographs fail to convey this, much of the fortress walls are concealed by a surrounding ditch making it difficult to appreciate the fortress without a visit in person. Setting the walls low like this was an important feature of fortifications built during the age of cannon, making the walls a difficult target for attacking gunners. The defenses are well laid out, clearly the work of an experienced military architect. The bastions are properly angled to deflect incoming artillery rounds, gun-ports are positioned to sweep the walls of attacking infantry. Taking this position from prepared defenders would be a difficult proposition indeed.
The effort of constructing this fortress in the middle of a jungle was not in vain, the fort was repeatedly attacked by various forces over the following centuries. Repeated attempts on the fortress were made during the 18th century by either pirates or Miskito Sambus forces, supplied and trained by the British. This culminated with an attack by a substantial force of British and Sambus in 1762. The fortress commander, Don José de Herrera y Sotomayor, had died only a few days before the attackers arrived. Expecting an easy victory the British demanded the surrender of the fortress, only to be refused. Led by the nineteen-year-old daughter of the commander, Rafaela Herrera and Lieutenant Don Juan de Aguilar y Santa Cruz, the defenders held off the attackers for six days until the British were forced to withdraw due to heavy casualties and disease.
During a later expedition the British did capture the fortress in 1780, occupying it for eight months and finally abandoning it in early 1781. Among the officers who led this attack was the 22 year old Captain Horatio Nelson, in command of the HMS Hinchinbrook.
Today the fortress is surrounded by the town of El Castillo. The town serves as a regional shopping destination and an obligatory stop for the many tourists who transit the river. Beside visiting the historical fortress atop the bluff the town offers easy access to the biological preserves just downriver. A large number of hotels serve this market and tours of the surrounding area are easily arranged.
Entry to the fort is currently C$50 ($1.80 US in 2015) with an extra C$25 for a photography permit. The decent little museum offers a concise history of the fort and the region, from pre-Columbian to the Vanderbuilt steamships that operated up the river and across the lake. While the main displays are in Spanish a smaller English translation is posted beside each display. You might also bring your bird book and binoculars as the trees around the fort are alive with local birds. Take your time here, learning the history, enjoying the view, or simply watching the vultures soaring in the updrafts around the fortress walls.